Typical dispatching algorithms for multicar elevator systems in buildings having more than 10 or 20 floors evaluate many factors to determine which car should be assigned to answer a newly entered hall call. The principle is to select a car that will provide satisfactory service to the new hall call without negatively impacting other passengers in the elevator system. Two major considerations in assignment logic is the remaining response time (RRT), which is the predicted amount of time it will take a car to reach a new hall call; and predicted waiting time (PWT), which is the sum of RRT and the amount of time that has already passed since the call was registered. In some cases, these values may be combined via two-dimensional fuzzy logic, to give an assignment value which is then combined (perhaps with fuzzy logic) with other dispatching considerations.
It has long been known that the tendency for elevator cars to become “bunched” detracts from good elevator service and results in unusually long waits for some calls. Elevator cars may be considered “bunched” when most of the cars in the group are in close physical proximity to each other, taking into account the direction of travel. Traditional anti-bunching techniques are based on the distance between each car and the car directions.